Engraving presses have existed for a relatively long time, with many designs remaining substantially unchanged since their invention. Automation is difficult without substantially redesigning the engraving press. Large printing presses including 3 and 4 color printing presses utilize feed through roller designs where the print is applied by a circular drum. This is similar to newspaper printing press designs. Engraving presses have not generally progressed to this point. Engraving presses must apply a force sufficient to deform and reshape the surface of an imprinted sheet. Circular drum technology is generally not fitted for this approach.
Numerous engraving presses are currently manually fed, with an operator physically positioning a sheet to be engraved in an engraving press. Several attempts of automating the sheet feeding process have been made.
U.S. Pat. No. 3,893,392, issued to Brenn, et. al., discloses an automatic feeding mechanism designed to feed envelopes into an engraving press. The Brenn apparatus consists of an envelope storage section located above the engraving area. A combination of vacuum actuated suction cups and a mechanical guide is raised to grab each envelope to be engraved. When lowered, this "apparatus" holds an envelope. The apparatus is then moved towards a belt feeder, and the vacuum from the suction cups released to that the envelope may travel in a belt feed mechanism consisting of an upper and lower belt. The mechanical guide to help grab the envelope helps maintain the position of the envelope as the envelope initially enters the belt feed mechanism. No guide or orientation apparatus ensures positioning once the envelope is grasped between the upper and lower belts.
An optical sensor detects the presence of an envelope traveling along the belt feed mechanism. The envelope interrupts a light transmitted beam from a light source to a sensor positioned. This interruption of the light beam causes the belt to stop. An engraving press is then actuated to imprint the envelope. Once the envelope is imprinted, the belt drive is released, and the envelope allowed to continue along the belt path. No positioning apparatus ensures that the envelope is properly located underneath the engraving press. The system relies on the optical sensor and immediate braking action to stop the belts, thus stopping the movement of the envelope at the precise location desired. The Brenn feeder relies heavily on electrical switches, combinational logic, and actuation of the mechanical apparatus by an electronic circuit in order to accomplish its function.
U.S. Pat. No. 2,825,281, issued to Haywood, discloses an apparatus for feeding sheets to a stamping apparatus, more commonly called an engraving press. Haywood uses a vacuum mechanism to lift individual sheets off a paper supply stack. The vacuum assembly is rotated and the sheets fed in between a pair of transfer rollers. The transfer rollers convey the sheet to the top of a transfer platform. The sheet rests on several belts which move along the surface of the transfer platform. The sheet comes to rest on the transfer platform when it comes into contact with stops which are located immediately above the belts on the top of the transfer platform. The sheet is then in position to exit the transfer platform at right angles to the transfer platform and the belts on which the sheet has been riding. Movable rollers come into contact with the edge of the sheet, causing the sheet to begin to travel along a second set of belts which are positioned at right angles to the first set of belts.
As the sheet travels along the second set of belts, it comes into contact with a stop. A roller maintaining contact between the sheet and belt is raised, and a bar pushes the sheet toward the printing head to position the sheet. Vertical rods are then lowered to hold the sheet in place, and the sheet is imprinted. During this process, the belts on which the sheets have been riding continue to move. After being imprinted, the sheet is released by the vertical rods, the stop is raised, and a roller lowered on top of the sheet to force the imprinted sheet to again move along the belts away from the imprinting area.
The Haywood apparatus employs a vacuum to load sheets onto the first table, and thereafter employs a series of mechanical arms linked to a cam arrangement in order to operate the bulk of the apparatus. A paper sensor is formed at the end of the first set of belts by placing a metal strip on top of the table such that when the sheet is fed into position against the positive stops located above the belts, an electrical circuit is mechanically interrupted by the sheet of paper.
Apparatus of the type described in Haywood and Brenn has been employed in order to more rapidly feed an engraving press, thereby reducing the number of manual operations required in order to imprint an envelope or other sheet.
This prior art fails to provide a reliable, repeatable, easy to use sheet feeder which can effectively replace manual operation. The prior art is also fairly difficult to set-up and maintain. The Brenn invention has a configuration specifically designed for envelopes. It cannot easily accommodate 81/2.times.11 sheets or other larger sheets which are less rigid than an envelope. The "top down" feed tray and mechanism cannot hold larger sheets, and the feed mechanism poorly adapted to feed highly flexible sheets. Positioning beneath the imprinting head is not repeatably assured. The sheet being fed may become tilted or otherwise shift position either in the feed tray or while being transferred to the on the sheets varying.
The Haywood invention requires two sets of belts positioned at right angles to each other. Mechanical stops in the sheet's path establish orientation of the sheet on the first set of belts. Subsequent transfer to a second set of belts at right angles to the first set may allow the orientation of the sheet to change. A single mechanical stop halts movement of the sheet, along the second set of belts. This mechanical stop must be accurately positioned or the sheet may rotate about the mechanical stop. The push bar must be similarly accurately positioned to prevent rotation of the sheet about the push bar.
Haywood also requires positive clamping by vertical rods to keep the sheet in place during imprinting. The Haywood apparatus is driven by a large number of mechanical rods and cams which must be precisely adjusted. A change in the size of the sheet requires redesign of numerous rods and cams.
Neither Brenn nor Haywood are oriented to accommodate printing on the lower surface of a sheet, which is a common press configuration.
The need therefore exists for a reliable sheet feeder which repeatably locates the sheet to be imprinted in precisely the same location for imprinting. A feeder is also needed which can easily accommodate a large variety of sheet sizes and rigidity, and is easy to operate.